1. Field of the Invention
This invention relates to forming metal coatings on glass fibers employed as optical waveguides, and more particularly, to employing laser heating of the glass fiber to deposit the metal by dissociation of a metal-containing compound, thereby coating only the glass fiber.
2. Description of the Invention
The deposition of metal to coat glass fibers is done for a variety of purposes. Often, the metal deposition is done as an aid to strengthening the fiber, or at least maintaining the strength of the fiber, for use in composite applications. In the case of glass fibers employed in optical communications and data links, the metal coating may additionally provide a metallic conduction path for electrical signals.
Deposition of metal coatings on glass fibers has been done from the solid phase (see, e.g., U.S. Pat. No. 3,650,598), from aqueous solution (see, e.g., U.S. Pat. Nos. 3,019,515, 2,979,424 and 2,900,274), from molten metal (see, e.g., U.S. Pat. Nos. 3,347,208 and 2,980,956) and from the vapor phase (see, e.g., U.S. Pat. Nos. 3,806,224, 3,097,941, 3,083,550 and 2,938,821). In vapor phase deposition, metal-containing compounds have been variously employed, in which the ligand is a carbonyl, halide, alkyl, aryl, olefin, ester, nitro compound, hydride and mixtures of these. In general, however, deposition of metal from such vapor phase has required passing the glass fiber to be coated through a chamber, introducing the metal-containing compound into the chamber and dissociating the metal-containing compound to form the metal plus a gaseous product. Dissociation is commonly carried out by heating the metal-containing compound to its dissociation point. In most instances, this has necessitated heating the entire structure (chamber, susceptor, gas phase, etc.) through which the glass fiber is passing. The deposition of metal thus occurs over all heated surfaces, including the walls of the chamber through which the glass fiber is being passed as well as the fiber itself. Such extraneous deposition is, of course, wasteful of material.